1. Field of the Invention
This invention relates to ROM memories.
2. Description of the Related Art
ROM memories include ROM memory cells that are utilized to permanently store data for electronic systems. With some types of ROM memory cells, a programmable element is programmed to store a logical 1 or logical 0 in a memory cell.
One type of ROM cell includes an NFET. The source terminal of the NFET is connected to ground, the drain terminal of the NFET is selectively coupled to a bit line via a programmable element, and the gate terminal of the NFET is connected to a word line. When the programmable element is in a programmed conductive state, the assertion of the word line generates a conductive path through the NFET to pull the bit line towards ground. When the programmable element is in a non conductive programmed state, the assertion of the word line does not generate a conductive path between the bit line and ground due to the programmable element being non conductive. Therefore, the bit line remains at a precharged voltage value when being read.
In another type of ROM cell, the drain terminal of an NFET is connected to VDD, the source terminal of the NFET is selectively coupled to a bit line via a programmable element, and the gate of the NFET is connected to a word line. When the programmable element is in a programmed conductive state, the assertion of the word line generates a conductive path through the NFET to pull the bit line towards VDD. When the programmable element is in a non conductive programmed state, the assertion of the word line does not generate a conductive path between the bit line and VDD due to the programmable element being non conductive. Therefore, the bit line remains at a precharged voltage value when being read.
The use of the same reference symbols in different drawings indicates identical items unless otherwise noted. The Figures are not necessarily drawn to scale.